Investigations into the role of dopamine (DA) in basal ganglia (BG) function in FY98 have focused on the role of dopamine in regulating firing rate and firing patterns in different basal ganglia nuclei in intact rats and in a rodent model of Parkinson's disease. There has been a growing interest in the importance of oscillatory firing patterns in the nervous system. However, most studies have only examined spike trains for oscillatory structure at frequencies greater than 1 Hz. In extracellular single unit recording studies, the Physiological Neuorpharmacology Section has found that many tonically-active neurons in 4 different basal ganglia nuclei have slow, recurrent oscillations in baseline firing rate in immobilized, awake rats. Rates oscillate by up to +/- 50% of average rate over a time scale of 10-60 seconds with mean oscillatory periods averaging ~30 s. Dopamine agonists profoundly affect these firing rate oscillations, increasing the numbers of cells which show periodic oscillations (to 87 100%) and increasing frequency and regularity (spectral peak power) of the oscillations; mean periods shift to ~15 s. The frequency of these oscillations is synergictically increased by D1 and D2 receptor stimulation and dopamine agonist modulation is reversed by either D1 or D2 antagonists. Significant slow periodicities in rate (either basal or post-agonist) have not been found in any basal ganglia neurons in chloral hydrate, ketamine or urethane-anesthetized rats, suggesting that this phenomena depends upon ongoing activity in afferent structures. The modulation of slow periodicities in basal ganglia neuronal firing rates by dopaminergic agonists suggests the involvement of these patterns in behaviors and cognitive processes that are affected by dopamine. Periodic rate oscillations in basal ganglia output nuclei are likely to strongly affect the firing patterns of target neurons. Modulation of slow, periodic oscillations in firing rate may be an important mechanism by which DA influences motor and cognitive processes in normal and dysfunctional states. In FY 99, the incidence and expression of these slow oscillations will be investigated in awake behaving rats, in animal models of Parkinson's disease and in spike trains from Parkinson patients recorded during pallidotomy procedures.